The circuitry on a semiconductor chip has to connect with other circuits. These may be chips or display devices, transducers or electromechanical devices. Each of these situations will require the imposition of circuitry to interface the chip to the external environment. This interface is supplied by bonding pads.
Physically, bonding pads are the squares of metal, typically aluminum, generally 100 to 150 microns square, that are connected to the pins of the semiconductor package with bonding wires. Bonding pads are normally positioned near to the chip edge. Toward the end of the semiconductor fabrication process, passivation coatings are applied to protect the fabricated device. Silicon oxide films are typically deposited, often pyrolytically, using layers of oxides such as oxynitride, silicon dioxide, phosphorus-silicate-glass, boron-phosphorus-silicate-glass, and the like.
Following deposition the silicon oxide must be removed from the bonding pad so that the fabricated device can interconnect with other circuits. An etching composition is typically employed to remove the passivation coating.
Conventional passivation etchants contain ammonium fluoride, acetic acid, water and additional additives such as ethylene glycol or aluminum acetate. Current processes seek to over-etch the bonding pads to ensure complete elimination of the silicon oxide passivating coating. Over-etching with current products results in significant roughing and pitting of the bonding pad surfaces, creating poor contact points to the detriment of device reliability because current products also attack underlying metal surfaces. The products are known to dissolve pads completely, increasing the manufacturing yield loss.
There exists a need for a selective silicon oxide passivation coating etchant that does not attack underlying metal surfaces.